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Abstract:

A process for compressing a hydrogen-sulfide-comprising gas stream, which
comprises (i) compressing the hydrogen-sulfide-comprising gas stream in
a compressor, (ii) flushing the compressor with a mixture comprising
dialkyl polysulfides, dialkyl disulfides and at least one amine; a
process for producing sulfur compounds, selected from the group
consisting of alkylmercaptans, dialkyl disulfides and alkanesulfonic
acids, which comprises the conversion of hydrogen-sulfide-comprising gas
streams, wherein the hydrogen-sulfide-comprising gas streams are
compressed according to the process comprising steps i) and ii); and also
the use of a mixture comprising dialkyl polysulfides, dialkyl disulfides
and at least one amine for removing sulfur deposits which occur in the
compression of hydrogen-sulfide-comprising gas streams.

Claims:

1-13. (canceled)

14. A process for compressing a hydrogen-sulfide-comprising gas stream,
the process comprising (i) compressing the hydrogen-sulfide-comprising
gas stream in a compressor, (ii) flushing the compressor with a mixture
comprising a) 10 to 98% by weight of at least one dialkyl polysulfide, b)
1.9 to 80% by weight of at least one dialkyl disulfide, and c) 0.1 to 10%
by weight of at least one amine, wherein a sum of dialkyl polysulfides,
dialkyl sulfides and amines totals 100% by weight.

15. The process of claim 14, wherein the compressor is a rotary gas
compressor.

16. The process of claim 14, wherein the compressing (i) proceeds in one
or two stages.

19. The process of claim 18, wherein the flushing of the compressor (ii)
proceeds at a temperature in a range of 30 to 160.degree. C.

20. The process of claim 14, wherein the mixture employed for the
flushing in (ii) comprises a) 20 to 95% by weight of at least one dialkyl
polysulfide; b) 4.8 to 72% by weight of at least one dialkyl disulfide;
c) 0.2 to 8% by weight of at least one amine; wherein a sum of dialkyl
polysulfides, dialkyl disulfides and amines totals 100% by weight.

21. The process of claim 14, wherein the hydrogen-sulfide-comprising gas
stream is obtained by producing hydrogen sulfide from the elements sulfur
and hydrogen.

22. A process for producing at least one selected from the group
consisting of an alkylmercaptan, a dialkylsulfide, and an alkyl sulfonic
acid, the processing comprising: compressing a
hydrogen-sulfide-comprising gas stream by the method of claim 14; and
subsequently reacting the compressed hydrogen-sulfide-comprising gas
stream to obtain the at least one selected from the group consisting of
an alkylmercaptan, a dialkylsulfide, and an alkyl sulfonic acid.

23. The process of claim 22, wherein the at least one alkylmercaptan is
produced, and the reacting comprises reacting at least one alkanol with
the compressed hydrogen-sulfide-comprising gas stream.

24. The process of claim 22, wherein the at least one dialkyl disulfide
is produced, and the reacting comprises: a) producing at least one
alkylmercaptan by reacting at least one alkanol with the compressed
hydrogen-sulfide-comprising gas stream; and b) converting the at least
one alkylmercaptan obtained in a) to at least one dialkyl disulfide by
oxidizing the alkylmercaptan with sulfur.

25. The process of claim 22, wherein the at least one alkanesulfonic acid
is produced, and the reacting comprises: a) producing at least one
alkylmercaptan by reacting at least one alkanol with the compressed
hydrogen-sulfide-comprising gas stream; b) converting the at least one
alkylmercaptan produced in a) to at least one dialkyl disulfide by
oxidizing the alkylmercaptan with sulfur; and c) oxidizing the dialkyl
disulfide obtained in b) to the at least one alkanesulfonic acid with an
oxidizing agent.

26. A method of removing at least one sulfur deposit produced in
compressing a hydrogen-sulfide-comprising gas stream, the method
comprising: contacting a mixture comprising at least one dialkyl
polysulfide, at least one dialkyl disulfide, and at least one amine with
the sulfur deposit.

27. The process of claim 14, wherein the compressor is a liquid ring
compressor.

28. The process of claim 14, wherein the compressor is a screw
compressor.

29. The process of claim 15, wherein the compressing (i) proceeds in one
or two stages.

Description:

[0001] The present invention relates to a process for compressing a
hydrogen-sulfide-comprising gas stream, which comprises [0002] (i)
compressing the hydrogen-sulfide-comprising gas stream in a compressor,
[0003] (ii) flushing the compressor with a mixture comprising dialkyl
polysulfides, dialkyl disulfides and at least one amine; a process for
producing sulfur compounds, selected from the group consisting of
alkylmercaptans, dialkyl disulfides and alkanesulfonic acids, which
comprises the conversion of hydrogen-sulfide-comprising gas streams,
wherein the hydrogen-sulfide-comprising gas streams are compressed
according to the process comprising steps i) and ii); and also the use of
a mixture comprising dialkyl polysulfides, dialkyl disulfides and at
least one amine for removing sulfur deposits which occur in the
compression of hydrogen-sulfide-comprising gas streams.

[0004] The compression of hydrogen-sulfide-comprising gas streams is a
frequent processing problem. Hydrogen sulfide is frequently used under
pressure. Thus, for example, the precipitation of heavy metals from
solution is carried out under pressure. As a result, precipitation
apparatuses having a small volume can be used. In addition, the synthesis
of alkylmercaptans by reacting hydrogen sulfide with alkanols is
customarily carried out using compressed hydrogen sulfide. The
alkylmercaptans can subsequently be further reacted, eg. to form dialkyl
sulfides and/or alkanesulfonic acids.

[0005] The hydrogen sulfide used in the abovementioned processes can, for
example, be obtained from an acid gas scrubber, from refinery processes
or by reaction of the elements sulfur and hydrogen. Because of the
toxicity of the hydrogen sulfide, attempts are made to keep not only the
amount of hydrogen sulfide which is handled in a production process, but
also the pressure at which the hydrogen sulfide is handled, as small as
possible. Therefore the hydrogen sulfide is customarily as far as
possible produced or provided at atmospheric pressure and not compressed
until the application stage.

[0006] In the compression of hydrogen-sulfide-comprising gas streams, it
is frequently observed that the compressor becomes blocked with sulfur
deposits. These can lead to a fall in compressor performance or, if the
compressor is operated further despite deposits, to mechanical damage on
the compressor.

[0007] One cause of the sulfur deposits is the entrainment of elemental
sulfur from the hydrogen-sulfide-comprising source used, which sulfur
deposits, in particular, on cold surfaces. A further cause is the
decomposition of polysulfanes (H2Sx, in particular to hydrogen
sulfide and sulfur) which are generally present in the
hydrogen-sulfide-comprising source.

[0008] An essential factor for the availability of production plants for
synthesizing alkylmercaptans and/or dialkyl disulfides and sulfonic acids
produced therefrom is therefore the availability of the compressor for
the hydrogen-sulfide-comprising gas.

[0009] One possible method of increasing the availability of the
compressor is the purification of hydrogen-sulfide-comprising gases
before introduction into the compressor.

[0010] For instance WO 2004/022482 relates to the purification of hydrogen
sulfide by porous media. According to WO 2004/022482,
hydrogen-sulfide-comprising gas obtained by reacting hydrogen and liquid
sulfur is passed for purification through a filter which comprises a
solid selected from activated carbon, aluminum oxide and silicon dioxide.
According to WO 2004/022482, the gas thus purified is capable of
depositing solid sulfur only to a slight extent, or not at all.

[0011] DE 102 45 164 A1 relates to a process for the conversion of
polysulfanes. These polysulfanes H2Sx occur in the synthesis of
hydrogen sulfide by reaction of hydrogen with sulfur. On compression of
the hydrogen-sulfide-comprising gas stream, an uncontrolled decomposition
of the polysulfanes to hydrogen sulfide and sulfur occurs, which leads to
unwanted sulfur deposits in the entire compression zone. According to DE
102 45 164 A1, the polysulfanes in the hydrogen-sulfide-comprising gas
from the synthesis by reaction of hydrogen and sulfur are catalytically
converted to hydrogen sulfide and sulfur by bringing the
hydrogen-sulfide-comprising gas into contact with catalytically active
solids, catalytically active liquids or gases. Suitable catalytically
active solids are, according to DE 102 45 164 A1, activated carbon,
Al2O3, SiO2, zeolites, glasses, oxides and mixed oxides,
alkali metal, alkaline earth metal and other basic mixtures or
hydroxides. Suitable catalytically active liquids are basic, aqueous or
alcoholic solutions of ammonia, amines or aminoalcohols, and also
solutions of alkali metal, alkaline earth metal or other basic oxides or
hydroxides, sulfides or hydrogensulfides. Suitable gases are ammonia,
amines or aminoalcohols.

[0012] A disadvantage of the abovementioned processes for purifying the
hydrogensulfide obtained from the reaction of hydrogen with sulfur is the
lasting consumption of the components used for the purification.

[0013] As an alternative, it is proposed to remove the sulfur-comprising
impurities in hydrogen-sulfide-comprising gases by condensation or
desublimation in heat exchangers operating in alternation which can then
be freed from sulfur deposits by heating, when required (see Ullmann's
Encyclopedia of Industrial Chemistry, Release 2008, 7th Edition, DOI:
10.1002/14356007.a13--467, chapter "Hydrogen Sulfide", section "4.1
Production by chemical reaction").

[0014] In principle, furthermore, mechanical cleaning of the compressor of
hydrogen sulfide deposits is possible. However, this is always associated
with an opening of the plant and potential emission of hydrogen sulfide.
Furthermore, the opening of the plant in the case of plants having toxic
media is associated with long shutdown times because of the preceding
cleaning processes.

[0015] The object of the present invention is therefore providing a
process for compressing hydrogen-sulfide-comprising gases having the
highest possible availability with respect to the compressor, which
process succeeds with the lowest capital expenditure possible.

[0016] This object is achieved by a process for compressing a
hydrogen-sulfide-comprising gas stream, which comprises [0017] i)
compressing the hydrogen-sulfide-comprising gas stream in a compressor,
[0018] ii) flushing the compressor with a mixture comprising dialkyl
polysulfides, dialkyl disulfides and at least one amine.

Step i)

[0019] A "compressor", for the purposes of the present invention, is to be
taken to mean not only the compressor itself but also its peripherals,
that is to say, in particular, the compressor and one or more attached
heat exchangers, e.g. shell and tube or plate heat exchangers, and also,
if appropriate, attached liquid separators.

[0020] As compressors in the present process, in principle all compressors
known to those skilled in the art are suitable. Preferably, in the
process according to the present invention, use is made of rotary gas
compressors, particularly preferably screw compressors, or liquid ring
compressors, wherein liquid ring compressors are very particularly
preferred. Rotary gas compressors, in particular screw compressors and
liquid ring compressors, are known to those skilled in the art.

[0021] The screw compressor falls under the rotary twin-shaft displacement
compressors having internal compression. The screw compressor can have a
single-stage or two-stage construction. For cooling the
hydrogen-sulfide-comprising gas stream which is to be compressed, during
the compression, an injection medium can be sprayed in. The injection can
proceed upstream of the first and/or second stage. As injection medium,
use can be made of, for example, water or an alcohol (for example
methanol in the production of methylmercaptan). The injection medium
vaporizes in part or completely during the injection and compression
process and thereby cools the process gas. After the compression, the
injection medium can be condensed or left in the process gas (one example
for compression in the screw compressor using methanol as injection
medium is disclosed, for example, in DE-A 196 54 515). In the case of
condensation of the injection medium and/or cooling, it can be used again
as injection medium, if appropriate after filtration.

[0022] The liquid ring compressor which is particularly preferably used in
the process according to the invention is a rotary displacement
compressor of single-shaft type. The ring liquid used in the liquid ring
compressor used according to the process according to the invention can
be, for example, water or the mixture which is used according to the
invention for flushing the compressor and comprises dialkyl polysulfides,
dialkyl disulfides and at least one amine. In a preferred embodiment,
water is used as ring liquid. Ring liquid entrained in the compression
process is separated off in a liquid separator (demistor, apparatus for
separation of gas and liquid) after it leaves the compressor, passed
through a heat exchanger for cooling and from there conducted back into
the compressor. Suitable heat exchangers are, for example, shell and tube
heat exchangers or plate heat exchangers. In the case of the liquid ring
compressor, the sulfur deposits occur on compression of the
hydrogen-sulfide-comprising gas stream in particular in the liquid ring
compressor itself and also in the heat exchanger or heat exchangers.

[0023] The compression in step i) of the process according to the
invention can proceed in a single stage, two-stage or multistage manner.
Preferably, the compression proceeds in a single or two-stage manner.

[0024] A compressor which has no sulfur deposits generally has a
compressor output which is so high that more gas is compressed than is
needed for the subsequent step. The excess compressed gas is recirculated
via a bypass around the compressor from the pressure side to the suction
side of the compressor (and fed back to the compressor). In the case when
the compressor is blocked with sulfur deposits, the compressor output
decreases with the amount of sulfur deposits in the compressor. This
means that less gas is recirculated to the compressor via the bypass. If
the compressor output is so low owing to the sulfur deposits that no gas
is recirculated any more via the bypass, the compressor must be flushed.

Operating Conditions of the Compressor

[0025] The entry pressure into the compressor is generally 700 mbar to
3000 mbar absolute, preferably 1000 to 2000 mbar absolute, particularly
preferably 1100 to 1500 mbar absolute. The exit pressure from the
compressor is generally 1000 to 7000 mbar absolute, preferably 1500 to
4000 mbar absolute, particularly preferably 2000 to 3200 mbar absolute,
very particularly preferably 2200 to 2800 mbar absolute, wherein the
entry pressure is lower than the exit pressure. The pressure conditions
in the compressor used in the process according to the invention differ
thereby substantially from the pressure conditions in a borehole in which
pressures of about 80 bar customarily prevail.

[0026] The entry pressure into the compressor is generally 10 to
70° C., preferably 15 to 50° C., particularly preferably 20
to 30° C. The exit temperature from the compressor is generally 15
to 200° C., preferably 20 to 100° C., particularly
preferably 25 to 50° C., very particularly preferably 30 to
40° C. Generally, the entry temperature is lower than the exit
temperature.

Hydrogen-Sulfide-Comprising Gas Stream

[0027] The hydrogen-sulfide-comprising gas stream passed through the
compressor can be produced by any process known to those skilled in the
art. The gas stream can originate either from the acid gas scrubber or
from refinery processes or can be obtained from the elements sulfur and
hydrogen. Preferably, the hydrogen-sulfide-comprising gas stream is
produced from the elements sulfur and hydrogen in the presence of a
catalyst, or non-catalytically. Suitable processes for producing the
hydrogen-sulfide-comprising gas stream are known to those skilled in the
art.

[0028] By way of example, a hydrogen-sulfide-comprising gas stream is
produced according to the prior art by the H2S process of Girdler
(Ullmann's Encyclopedia of Industrial Chemistry, 6th Edition, 2003, Vol.
17, page 291). In this process, H2S is produced non-catalytically
from the elements sulfur and hydrogen in a column having internals and in
an essentially horizontally directed expanded bottom phase. Into the
bottom phase which is filled with boiling sulfur, hydrogen is introduced
which strips into the ascending gas phase. Hydrogen and ascending sulfur
react in the gas space of the column, wherein the heat of reaction thus
liberated is removed from the product gas by scrubbing with liquid
sulfur. For this, liquid sulfur is taken off from the bottom phase of the
column, mixed with fresh cold sulfur and applied to the top of the
column. The product gas, which comprises substantially hydrogen sulfide,
is cooled in two heat exchangers.

[0029] A catalytic production of hydrogen sulfide is described, for
example, in Angew. Chem., Volume 74, 1962; No. 4; page 151. In this
process, hydrogen is passed into an externally heated sulfur bath. The
hydrogen loaded with sulfur vapor enters through boreholes into a
catalyst space. Incompletely reacted sulfur is, after it leaves the
catalyst space, condensed in an upper part of the hydrogen sulfide outlet
tube and passes back into the sulfur bath via a return tube. The catalyst
space is arranged concentrically around the hydrogen sulfide outlet tube.

[0030] Other examples of a catalytic production of hydrogen sulfide from
the elements sulfur and hydrogen are described in DE 1 113 446 and U.S.
Pat. No. 2,863,725.

[0031] DE 1 113 446 describes the catalytic production of hydrogen sulfide
by reaction of a stoichiometric mixture of hydrogen and sulfur in the
presence of a cobalt and molybdenum salt on a support comprising catalyst
at temperatures below 500° C., preferably between 300 and
400° C. The catalyst in this case is arranged in tubes through
which the mixture of hydrogen and sulfur flows.

[0032] According to U.S. Pat. No. 2,863,725 hydrogen sulfide is produced
from hydrogen and sulfur in the presence of a molybdenum-comprising
catalyst, wherein gaseous hydrogen is passed into a reactor comprising a
sulfur melt and ascends through the sulfur melt in the form of gas
bubbles.

[0033] The sulfur-comprising gas stream is customarily produced at
pressures of 0.7 to 2 bar, preferably 0.9 to 1.5 bar, very particularly
preferably 1 bar to 1.4 bar absolute.

[0034] The temperature of the hydrogen-sulfide-comprising gas stream
obtained after the production is generally 10 to 60° C.,
preferably 15 to 50° C., particularly preferably 20 to 45°
C., very particularly preferably 25 to 40° C.

[0035] In the case of the syntheses of hydrogensulfide from hydrogen and
sulfur, polysulfanes (H2Sx) are generally found as by-products
in the hydrogen-sulfide-comprising crude gas stream, obtained in an
amount of generally 10 to 200 ppm by weight, preferably 15 to 100 ppm by
weight, particularly preferably 20 to 75 ppm by weight, very particularly
preferably 25 to 50 ppm by weight.

[0036] The polysulfanes are removed from the hydrogen-sulfide-comprising
gas stream preferably before carrying out the process according to the
invention for compressing the hydrogen-sulfide-comprising gas stream.
This can proceed, for example, by one of the processes described in the
abovementioned documents WO 2004/022482 or DE 102 45 164 A1. It is
likewise possible to purify the polysulfanes by passing them through a
porous material (activated carbon filter or molecular sieve), for example
as disclosed in WO 2008/087125.

[0037] In addition, in a preferred embodiment, a further prepurification
of the hydrogen-sulfide-comprising gas stream proceeds by desublimation
in a heat exchanger. The gas leaving the desublimator has preferably a
molecular sulfur fraction of 0.001 to 5 ppm by weight, particularly
preferably 0.005 to 2 ppm by weight, very particularly preferably 0.01 to
1 ppm by weight.

[0038] The purity of the hydrogensulfide (hydrogen-sulfide-comprising gas
stream) used in the process according to the invention for compression is
generally 90 to 99.9% by volume, preferably 95 to 99.8% by volume,
particularly preferably 98 to 99.7% by volume, and very particularly
preferably 99 to 99.6% by volume.

Step ii)

[0039] Step ii) according to the invention comprises flushing the
compressor with a mixture comprising dialkyl polysulfides, dialkyl
disulfides and at least one amine.

[0040] The use of dialkyl polysulfides as solvent for dissolution of
sulfur deposits in lines which serve for the transport of
sulfur-comprising materials, in particular deposits in the extraction of
natural gas from high-sulfur natural gas sources, is known to those
skilled in the art, for example from DE 36 10 580 A1. There, a process is
described for dissolving sulfur by means of a liquid dialkyl polysulfide,
wherein the solvent comprises a dimethyl polysulfide mixture comprising 1
to 3% by weight of dimethyl disulfide, 35 to 45% by weight of
CH3SXCH3, wherein x has a value from 3 to 5, and the
remainder homologous polysulfides, wherein x has a value of 6 or more and
in particular 6 to 8. In addition, the dialkyl polysulfide used can
comprise 2 to 10% by weight of an amine, amide, mercaptan and/or
mercaptide. The solvent disclosed in DE 36 0 580 A1 serves for dissolving
sulfur deposits which can occur in lines which serve for the transport of
sulfur-comprising materials. In this case the problem of sulfur
sedimentation is of particular importance according to DE 36 10 580 A1 in
high-sulfur natural gas sources, wherein the high sulfur-content gases
lead to sulfur deposits on the inner walls of the pipelines. According to
DE 36 10 580 A1, dimethyl disulfide (DMDS) has a considerable dissolving
power for sulfur. Since it is necessary for continuous cleaning that the
composition of the solvent used remains substantially constant, it is
necessary to regenerate the dimethyl disulfide customarily used in the
prior art by breaking down the higher polysulfides taken up during the
cleaning. According to DE 36 10 580 A1, it has been found that as
alternative to dimethyl disulfide, use can be made of dimethyl
polysulfide mixtures having the special abovementioned composition for
removing sulfur deposits in lines with serve for the transport of
sulfur-comprising materials.

[0041] However, whereas DE 36 10 580 A1 relates to a process for
dissolving sulfur in lines which conduct the hydrogen-sulfide-comprising
gases from high-sulfur natural gas sources, the present invention relates
to a process for compressing hydrogen-sulfide-comprising gases, which
comprises flushing the compressor with a mixture comprising dialkyl
polysulfides, dialkyl disulfides and at least one amine. The temperature
and pressure conditions which prevail in the lines according to DE 36 10
580 A1, and also the hydrogen-sulfide-comprising gas streams used differ
considerably from the conditions occurring in the compression of
hydrogen-sulfide-comprising gases and the hydrogen-sulfide-comprising gas
streams used. In addition, the devices on which the sulfur deposits are
observed are also different. Whereas DE 36 10 580 A1 relates to the
problems of sulfur deposition in pipelines, the present application
relates to the problem of sulfur deposits in compressors, which also
include the peripherals of the compressor, for example heat exchangers.
The compressors and, in particular, the heat exchangers which are
attached to the compressors are distinguished in that they have narrow
gaps. A person skilled in the art would use low-viscosity flushing
solutions for cleaning the gaps.

[0042] The suitability of mixtures which comprise dialkyl polysulfides,
dialkyl disulfides and at least one amine for flushing the compressor is
therefore not obvious in the knowledge of DE 36 10 580 A1, in particular
for the following reasons:

[0043] In boreholes, pressures of about 80 bar generally prevail, whereas
the compressor is generally operated at an entry pressure of 700 mbar to
3000 mbar absolute and an exit pressure of 1000 to 7000 mbar absolute.

[0044] In addition, the structural conditions in boreholes, wherein these
are generally tubes of several cm in diameter, differ significantly from
the structural conditions of a compressor and peripherals thereof, which
generally has narrow gaps in the mm range.

[0045] These differences lead to the fact that a person skilled in the art
would not use, for flushing a compressor and peripherals thereof, the
high-viscosity mixtures according to DE 36 10 580 A1 which are suitable
for flushing boreholes, since these high-viscosity mixtures, under the
pressure conditions prevailing in the compressor, can pass only with
difficulty into the narrow gaps of the compressor and likewise can be
washed out again with difficulty.

[0046] Therefore, a person skilled in the art, would rather use the
essentially lower-viscosity solutions containing dialkyl disulfides for
flushing the compressor, which are customarily used for removing sulfur
deposits in boreholes, as found in the publication "Production challenges
in developing sour gas reserves", Chemical Engineering World 24(3),
87-93, Hyne. J. B., where dimethyl disulfide is shown to the best solvent
for sulfur (page 91) in the application in sour gas boreholes.

[0047] The dialkyl disulfides customarily used for removing sulfur
deposits in boreholes, however, surprisingly proved not to be very
suitable for the rapid and lasting removal of sulfur deposits in a
compressor, as the comparative examples in the present application show.
Surprisingly, it has been found that with the mixture used according to
the invention comprising dialkyl polysulfides, dialkyl disulfides and at
least one amine, despite the high viscosity, significantly better results
are achieved for the rapid and lasting removal of sulfur deposits in a
compressor.

[0048] Moreover, the different pressure and temperature conditions in the
pipelines according to DE 36 10 580 A1 and in the compressor according to
the present application have the effect that the sulfur deposits in the
respective devices can have different modifications. Different sulfur
modifications display a markedly differing solution behavior. Rhombic
sulfur S8, for example, exhibits a significantly higher reactivity
and solubility than what is termed μ sulfur. It is known that rapid
subcooling on cold surfaces, for example on heat-exchange surfaces, leads
to μ sulfur. The type of sulfur deposition and therefore the
solubility of the sulfur deposits depends essentially on the temperature
history and the origin of the hydrogen-sulfide-comprising gas from which
the sulfur deposits result. Experience on removal of sulfur deposits from
a hot borehole therefore cannot be readily applied to the removal of
sulfur deposits in a compressor. These are two completely different
technical fields.

[0049] Flushing the compressor according to step ii) of the process
according to the invention can proceed continuously or discontinuously.

[0050] In the case of continuous flushing, the compressor is freed
continuously from the sulfur deposits using the mixture used according to
the invention comprising dialkyl polysulfides, dialkyl disulfides and at
least one amine. In this case, the mixture used according to the
invention is added, e.g., when a liquid ring compressor is used, to the
ring liquid which is recirculated to the compressor. A continuous
procedure of the process according to the invention when other
compressors are used is possible without problem for a person skilled in
the art on the basis of his knowledge. The pressure and temperature
conditions in the compressor in the case of the continuous procedure
correspond to the abovementioned pressure and temperature conditions in
the compressor.

[0051] In the case of the discontinuous flushing, the compressor is shut
down for a short time for cleaning work and treated using the mixture
used according to the invention comprising dialkyl polysulfides, dialkyl
disulfides and at least one amine.

[0052] Customarily, the discontinuous flushing of the compressor with the
mixture used according to the invention comprising dialkyl polysulfides,
dialkyl disulfides and at least one amine proceeds in the form that the
mixture in liquid form flows through the compressor. The temperature in
the flushing operation is generally 30 to 160° C., preferably 40
to 140° C., particularly preferably 60 to 120° C., very
particularly preferably 75 to 110° C., and especially very
particularly preferably 90 to 100° C.

[0053] In the case of discontinuous flushing, the compressor is filled in
part or completely with the mixture used for the flushing. Preferably,
the filling is complete. In the case of discontinuous flushing the
flushing times are from 5 minutes to 1 hour, preferably 10 minutes to 50
minutes, particularly preferably 20 minutes to 40 minutes.

Dialkyl Disulfides and Dialkyl Polysulfides

[0054] Suitable alkyl groups of the dialkyl disulfides and dialkyl
polysulfides are, independently of one another in each dialkyl disulfide
and/or dialkyl polysulfide, customarily C1-C14 alkyl moieties,
preferably C1-C6 alkyl moieties, particularly preferably
C1-C3 alkyl moieties. Very particularly preferably the alkyl
moieties are methyl, ethyl, n-propyl or isopropyl, very particularly
preferably the alkyl moieties are methyl moieties. The alkyl moieties in
the dialkyl polysulfides and/or dialkyl disulfides can in each case be
identical or different. Preferably, they are identical. Particularly
preferably the dialkyl polysulfides used in the process according to the
invention are dimethyl polysulfides and the dialkyl disulfides are
dimethyl disulfide.

[0055] Suitable dialkyl polysulfides have the general formula
R--SX--R', wherein R and R' are the abovementioned alkyl moieties. x
in the dialkyl polysulfides means 3 to 12, preferably 3 to 10.
Customarily, the dialkyl polysulfides are present in the form of mixtures
of dialkyl polysulfides having various chain lengths.

Amines

[0056] The at least one amine which is comprised in the mixture used in
step ii) according to the invention for flushing can be a primary,
secondary or tertiary aliphatic or aromatic amine. Preferably, use is
made of primary, secondary or tertiary aliphatic amines. Particular
preference is given to liquid or solid amines which have a low water
solubility. Very particularly preferably the amines are primary,
secondary or tertiary amines having 6 to 60 carbon atoms. Examples of
suitable amines are tridecylamine, fatty amines such as
N,N-dimethyl-C12/C14-amine, and also dicyclohexylamine.

[0057] The mixtures which are used according to the invention in step ii)
for flushing and which comprise dialkyl polysulfides, dialkyl disulfides
and at least one amine, in a preferred embodiment, comprise [0058] a) 10
to 98% by weight, preferably 20 to 95% by weight, particularly preferably
35 to 90% by weight, of dialkyl polysulfides; [0059] b) 1.9 to 80% by
weight, preferably 4.8 to 72% by weight, particularly preferably 9.5 to
60% by weight, of dialkyl disulfides; [0060] c) 0.1 to 10% by weight,
preferably 0.2 to 8% by weight, particularly preferably 0.5 to 5% by
weight, of at least one amine; wherein the sum of dialkyl polysulfides,
dialkyl disulfides and at least one amine totals 100% by weight.

[0062] Depending on whether the flushing in step ii) of the process for
compression according to the invention is carried out continuously or
discontinuously, the composition of the dialkyl polysulfide containing
mixture which is preferably used can vary.

[0063] In a preferred embodiment of step ii) of the process according to
the invention, use is made of mixtures comprising: [0064] a) 50 to 98% by
weight, preferably 70 to 95% by weight, particularly preferably 80 to 90%
by weight, of dialkyl polysulfides; [0065] b) 1.9 to 40% by weight,
preferably 4.8 to 22% by weight, particularly preferably 9.5 to 15% by
weight, of dialkyl disulfides; [0066] c) 0.1 to 10% by weight, preferably
0.2 to 8% by weight, particularly preferably 0.5 to 5% by weight, of at
least one amine; wherein the sum of dialkyl polysulfides, dialkyl
disulfides and at least one amine totals 100% by weight.

[0067] The mixture mentioned above is used particularly preferably when
step ii) of the process according to the invention is carried out
discontinuously.

[0068] In a further preferred embodiment of step ii) of the process
according to the invention, use is made of mixtures comprising: [0069] a)
10 to 70% by weight, preferably 20 to 60% by weight, particularly
preferably 35 to 50% by weight, of dialkyl polysulfides; [0070] b) 29.9
to 80% by weight, preferably 38.8 to 72% by weight, particularly
preferably 49.5 to 60% by weight, of dialkyl disulfides; [0071] c) 0.1 to
10% by weight, preferably 0.2 to 8% by weight, particularly preferably
0.5 to 5% by weight, of at least one amine; wherein the sum of dialkyl
polysulfides, dialkyl disulfides and at least one amine totals 100% by
weight.

[0072] The mixture mentioned above is used particularly preferably when
step ii) of the process according to the invention is carried out
continuously.

[0073] The mixture used in step ii) can in addition comprise small amounts
of other components, for example small amounts of alkylmercaptan and
hydrogen sulfide. In a preferred embodiment, the mixtures, in addition to
the abovementioned small amounts present if appropriate of alkylmercaptan
and hydrogen sulfide, do not contain any other components. In particular,
the mixtures used for flushing, in a preferred embodiment of the present
invention, do not comprise surfactants.

[0074] In a preferred embodiment of the present invention, the mixtures
used for flushing the compressor in step ii) are not mixtures which must
be prepared extra for the purpose of flushing, but are mixtures as are
obtained in processes for producing sulfur compounds starting from
hydrogen-sulfide-comprising gas compressed according to the process
according to the invention. Such sulfur compounds are, for example,
alkylmercaptans, dialkyl disulfides and alkanesulfonic acids.
Particularly preferably, the mixtures used for the flushing in step ii)
of the process according to the invention are the amine-containing crude
discharge from the dialkyl disulfide synthesis which can be carried out
according to processes known to those skilled in the art and will be
described in more detail hereinafter.

[0075] The process according to the invention for compressing a
hydrogen-sulfide-comprising gas stream, in one embodiment of the present
invention, is used in combination with the production of sulfur
compounds, in particular sulfur compounds selected from the group
consisting of alkylmercaptans, dialkyl disulfides and alkanesulfonic
acids. Therefore, the present invention further relates to a process for
producing sulfur compounds, selected from the group consisting of
alkylmercaptans, dialkyl disulfides and alkanesulfonic acids, which
comprises the conversion of a hydrogen-sulfide-comprising gas stream,
wherein the hydrogen-sulfide-comprising gas stream is compressed
according to the process according to the invention for compressing the
hydrogen-sulfide-comprising gas stream which comprises steps i) and ii).

Processes for Producing Alkylmercaptans

[0076] Processes for producing alkylmercaptan are known to those skilled
in the art. According to the invention, for producing the
alkylmercaptans, use is made of a compressed hydrogen-sulfide-comprising
gas stream, wherein the compression of the hydrogen-sulfide-comprising
gas stream used for the production of the alkylmercaptans comprises the
steps i) and ii). Preferably, the alkylmercaptans are produced by
reacting alkanols with a hydrogen-sulfide-comprising gas stream which is
compressed according to the process according to the invention comprising
the steps i) and ii).

[0077] The present invention therefore further relates to a process for
producing alkylmercaptans, which comprises the steps: [0078] i)
compressing the hydrogen-sulfide-comprising gas stream in a compressor,
wherein a compressed hydrogen-sulfide-comprising gas stream is obtained;
[0079] ii) flushing the compressor with a mixture comprising dialkyl
polysulfides, dialkyl disulfides and at least one amine; [0080] iii)
reacting the compressed hydrogen-sulfide-comprising gas stream obtained
in step i) with one or more alkanols.

[0081] The steps i) and ii) have been described hereinbefore.

Step iii)

[0082] The reaction in step iii) can be carried out in this case by
customary processes known those skilled in the art. Suitable processes
are mentioned, for example, in DE 101 37 773 A1. Customarily, the
reaction of the alkanols with the compressed hydrogen-sulfide-comprising
gas stream proceeds in the presence of catalysts. Suitable catalysts are,
for example, disclosed in U.S. Pat. No. 2,874,129 (metal oxides of
thorium, zirconium, titanium, vanadium, tungsten, molybdenum or chromium
on a porous support, for example Al2O3 or pumice); EP-A 0 749
961 (alkali metal carbonate on Al2O3); EP-A 1 005 906 (catalyst
based on zirconium oxide doped with magnesium or alkaline earth metals),
EP-A 0 038 540 (zeolite catalyst having a reduced amount of alkali metal
cations), EP-A 0 564 706 (catalyst made of amorphous Al2O3 gel
and/or made from Al2O3 gel applied to an aluminum-comprising
material); U.S. Pat. No. 2,822,401 (activated Al2O3), U.S. Pat.
No. 2,820,062 (active Al2O3 having 1.5 to 15% by weight of
potassium tungstenate as promoter), DE 196 39 584 (active Al2O3
having 15 to 40% by weight of cesium tungstenate as promoter) and in U.S.
Pat. No. 5,874,630 (Al2O3 having 0 to 20% by weight of a
transition metal compound and 0.1 to 10% by weight of an alkali metal or
alkaline earth metal bicarbonate, -carbonate, -oxide- or hydroxide).
Preferably, use is made of catalysts based on Al2O3,
particularly preferably γ-Al2O3 which is if appropriate
doped with promoters. Suitable promoters are transition metal compounds
selected from the group consisting of WO3, K2WO4,
H2WO4, Cs2WO4, Na2WO4, MoO3,
K2MoO4, H2MoO4, Na2MoO4,
phosphotungstenate, phosphomolybdate and silicotungstenate. The fraction
of the promoter is in general 1 to 40% by weight, preferably 5 to 25% by
weight, based on the weight of the catalyst. In the alkylmercaptan
synthesis in step iii), as catalyst, use is made particularly preferably
of γ-Al2O3 which is doped with K2WO4 as
promoter. Preferred alkylmercaptans have alkyl moieties having 1 to 14
carbon atoms, particularly preferably 1 to 6 carbon atoms, very
particularly preferably 1 to 3 carbon atoms, that is to say methyl,
ethyl, n-propyl or isopropyl moieties. Therefore, the alkanols ROH used
in step iii) of the process for producing alkylmercaptans are the
corresponding alkanols.

[0083] Generally, step iii) for producing alkylmercaptans is carried out
as a gas phase reaction. In this case, the alkanol and the
hydrogen-sulfide-comprising gas stream are customarily heated to a
temperature which is sufficiently high that not only the alkanol but also
the desired alkylmercaptan are present in the vapor phase. In this case,
the temperature must not be selected to be so high that decomposition of
the alkylmercaptan occurs. Generally, the process according to step iii)
is carried out at temperatures between 250 and 500° C., preferably
between 300 and 450° C. The pressure is generally 1 to 25 bar,
preferably 1 to 10 bar absolute.

[0084] The resultant alkylmercaptans can be reacted directly further to
give dialkyl disulfides. In addition, the alkylmercaptans can be used for
producing alkanesulfonic acids.

[0085] In a preferred embodiment, the "crude mercaptan stream" which is
produced using the abovementioned process, that is to say a mercaptan
stream which is not purified by extraction or distillation and which can
comprise incompletely reacted hydrogen sulfide, water and, as minor
components, dialkyl sulfide, small amounts of alkanol and dialkyl ether,
is further used for producing dialkyl disulfides.

Production of Dialkyl Disulfides

[0086] The dialkyl sulfides can be produced by any desired processes known
to those skilled in the art provided that they comprise a step for
compressing hydrogen-sulfide-comprising gas streams. The
hydrogen-sulfide-comprising gas streams are compressed according to the
process according to the invention comprising the steps i) and ii).

[0087] In a preferred embodiment, the dialkyl disulfides are produced by a
process which comprises [0088] a) producing alkylmercaptans comprising
the steps i), ii) and iii) which are mentioned hereinbefore, and [0089]
b) converting the alkylmercaptans obtained in step a) to dialkyl
disulfides by oxidation with sulfur.

Step a)

[0090] The alkymercaptans are produced in step a) as has been described
hereinbefore with respect to production of alkylmercaptans.

Step b)

[0091] When the dialkyl disulfides are produced by a process comprising
the steps a) and b), in step b) the reaction of the alkylmercaptans
obtained in step a) proceeds preferably with sulfur dissolved in an
organic disulfide with catalysis by an amine. Suitable amines are the
amines which are mentioned hereinbefore with respect to those in the
mixture which is used for flushing in step ii) of the process according
to the invention.

[0092] Customarily, step b) is carried out in a reaction column, wherein
the low-boilers which occur are recirculated to step a).

[0093] In a preferred embodiment, step b) of the abovementioned process is
followed by phase separation of the resultant mixture of aqueous phase,
which is ejected, and organosulfur phase.

[0094] Subsequently, in a further preferred embodiment, the organosulfur
phase is purified, which phase comprises, if appropriate, low-boilers,
the desired organic disulfide, polysulfides, amine and small amounts of
further by-products, wherein the organic disulfide is taken off, if
appropriate low-boilers which occur are recirculated to step (a) and
polysulfides which occur and amine are recirculated to step (b), with
addition of sulfur and, if appropriate, amine, wherein the phase
separation and the ejection of the aqueous phase can proceed subsequently
to step (a) or step (b).

[0095] The organic disulfide used as solvent in step (b) is preferably the
organic disulfide which is to be produced.

[0096] A particularly suitable process for producing the dialkyl
disulfides is mentioned in DE 198 54 427 A1, in which in step a) the
reaction of alkanols with hydrogen sulfide proceeds in the presence of a
suitable catalyst to give a "crude mercaptan stream" comprising
mercaptan, water, hydrogen sulfide and also small amounts of other
by-products such as organic sulfide and ether, and in the subsequent step
b) the reaction of the "crude mercaptan stream" with sulfur dissolved in
an organic disulfide proceeds with catalysis by an amine. According to
the invention, the hydrogen sulfide used in step a) is compressed
according to the process comprising the steps i) and ii).

[0097] A further preferred process for producing dialkyl disulfides is
disclosed in DE 101 16 817 A1, in which the production of organic
disulfides in a column equipped with temperature-controllable trays from
a crude mercaptan stream without prior separation by distillation is
mentioned. According to the invention, the hydrogen sulfide is compressed
by a process comprising the steps i) and ii) which are mentioned
hereinbefore.

Production of Alkanesulfonic Acids

[0098] The present invention further relates to a process for producing
alkanesulfonic acids, which is likewise carried out starting from
hydrogen-sulfide-comprising gas streams which are compressed according to
the invention.

[0099] Suitable processes for producing alkanesulfonic acids starting from
compressed hydrogen sulfide gas streams are known to those skilled in the
art.

[0100] In a preferred embodiment, the alkanesulfonic acids are produced by
a process which comprises

a) producing alkylmercaptans by a reaction with alkanols with a gas
stream which is compressed according to the compression process according
to the invention comprising the steps i) and ii); b) converting the
mercaptans produced in step a) to dialkyl disulfides by oxidation with
sulfur; and c) oxidizing the dialkyl disulfides obtained in step b) to
alkanesulfonic acid using an oxidizing agent.

[0101] The steps a) and b) correspond in this case to the steps a) and b)
mentioned with respect to the production of dialkyl disulfides.

[0102] The oxidation in step c) can be achieved using various oxidizing
agents. For instance, the oxidizing agents used can be hydrogen peroxide,
chlorine, dimethyl sulfoxide, mixtures of dimethyl sulfoxide and
hydroiodic acid and also nitric acid or mixtures of said oxidizing
agents. In addition, electrochemical oxidation is possible. Suitable
processes for producing alkanesulfonic acids by oxidizing the
corresponding dialkyl disulfides are known to those skilled in the art
and are disclosed, for example, in WO 98/34914, U.S. Pat. No. 2,697,722,
U.S. Pat. No. 2,727,920 and WO 00/31027.

[0103] It is essential in the case of the abovementioned processes for
producing sulfur compounds, selected from alkylmercaptans, dialkyl
disulfides and alkanesulfonic acids, that this process comprises a step
for compressing a hydrogen-sulfide-comprising gas stream, wherein the
compression of the hydrogen-sulfide-comprising gas stream is carried out
in accordance with the process according to the invention comprising the
steps i) and ii).

[0104] In a particularly preferred embodiment, the present invention
relates to a process for producing dialkyl disulfides, in particular a
process for producing dialkyl disulfides which comprises the steps (a)
and (b) as listed hereinbefore.

[0105] The compressor in the process according to the invention for
producing dialkyl disulfides is preferably flushed with a mixture
comprising dialkyl disulfides, dialkyl polysulfides and at least one
amine, wherein this mixture is the amine-comprising crude discharge from
the dialkyl disulfide synthesis. In this case, preferred compositions of
the crude discharge are mentioned hereinbefore for discontinuous flushing
or continuous flushing in each case. The mixture used for the flushing
can, after the flushing in step ii) of the process according to the
invention, be recirculated back to the process for producing dialkyl
disulfides, generally to the bottom phase of the dialkyl disulfide
purifying distillation (preferably in the discontinuous flushing process
in step ii)) or to the bottom phase of the dialkyl disulfide reaction
column after removal of the aqueous phase (preferably in the continuous
flushing process in step ii)).

[0119] The symbols x and xx indicate at what points the amine-comprising
crude discharge is preferably taken off for flushing in step ii) of the
compression process according to the invention. In this case, the point
designated x shows the takeoff point from the bottom phase of the dialkyl
disulfide purifying distillation, i.e. of the mixture which is preferably
used for the discontinuous flushing, and the point designated xx shows
the takeoff point from the bottom phase of the dialkyl disulfide reaction
column after removal of the aqueous phase, i.e. of the mixture which is
preferably used for continuous flushing.

[0120] It is clear from the process diagram in FIG. 1 that the mixture
which is preferably used for discontinuous flushing in step i) of the
compression process preferably corresponds to the bottom phase of the
dialkyl disulfide purifying distillation from the last column D of the
dialkyl disulfide synthesis. The mixture which is preferably used for the
continuous flushing in step ii) of the compression process according to
the invention preferably corresponds to the bottom phase from column B
after phase separation in the phase separator C, wherein the aqueous
phase is separated off and the organic phase is used for flushing.

[0121] An essential advantage of the process according to the invention is
that the mixture used for flushing the compressor need not be produced in
a complex manner, but corresponds to the amine-comprising crude discharge
from the dialkyl disulfide synthesis. This is an advantage, in
particular, when the compressed hydrogen-sulfide-comprising gas stream is
used for the production of dialkyl disulfides.

[0122] The hydrogen-sulfide-comprising gas which is passed through the
compressor in the production of the abovementioned sulfur compounds does
not generally correspond to the pure hydrogen-sulfide-comprising gas
stream which is used at the start of the process but is a circulated gas
which customarily comprises 60 to 90% by weight, preferably 70 to 80% by
weight, of hydrogen sulfide, 2 to 20% by weight, preferably 5 to 15% by
weight, of dimethyl sulfide and also small amounts of carbon monoxide,
methylmercaptan and dimethyl ether.

[0123] The present invention further relates to the use of a mixture
comprising dialkyl polysulfides, dialkyl disulfides and at least one
amine for removing sulfur deposits which occur in the compression of
hydrogen-sulfide-comprising gas streams. These sulfur deposits occur in
this case generally in the compressor, wherein compressor is taken to
mean not only the compressor itself but also its peripherals--as listed
hereinbefore. Mixtures which are preferably used and also compression
processes which are preferably carried out are mentioned hereinbefore.

[0124] The examples hereinafter additionally describe the invention.

EXAMPLES

[0125] The examples are carried out in each case using a liquid ring
compressor having a plate heat exchanger for cooling the ring liquid and
possibility for bypass, which compressor has sulfur deposits from
compression operations carried out on H2S which originates from the
synthesis from the elements and is used in a process for the synthesis of
methylmercaptan. The sulfur deposits are identical in the examples and
comparative examples.

1. Comparative Example

Discontinuous Flushing

[0126] For the discontinuous flushing, the compressor and peripherals
thereof are shut off and filled with dimethyl disulfide which is known as
a good solvent for sulfur. The compressor, after an exposure time of 30
minutes, at a temperature of 90° C., is free for further operation
of 3 weeks.

2. Example According to the Invention

Discontinuous Flushing

[0127] As in example 1, the compressor and peripherals thereof are shut
off. Instead of dimethyl disulfide, the compressor, however, is filled
with a polysulfide solution from the bottom phase of the dimethyl
disulfide purifying distillation. For this, the compressor and
peripherals thereof are filled with the bottom phase discharge. After an
exposure time of 30 minutes at a temperature of 90° C., compressor
and peripherals thereof are free for further operation of the plant of 3
months. The flushing liquid is recirculated to the bottom phase of the
dimethyl disulfide purifying distillation.

3. Example According to the Invention

Continuous Flushing

[0128] For the continuous flushing, the organic phase from the phase
separator downstream of the dimethyl disulfide crude column is used. For
this, 0.5 to 10 kg, preferably 1 to 5 kg, of organic phase are taken off
from the phase separator per 100 kg of hydrogen sulfide which is to be
compressed and fed into the compressor on the suction side or the ring
liquid feed when a liquid ring compressor is used. The liquid phase which
is separated off downstream of the compressor is preferably recirculated
to the bottom phase of the dimethyl disulfide reaction column.